Assignment of values for natural ecological benefits and anthropocentric ecosystem services in ri... more Assignment of values for natural ecological benefits and anthropocentric ecosystem services in riverine landscapes has been problematic, because a firm scientific basis linking these to the river's physical structure has been absent. We highlight some inherent problems in this process and suggest possible solutions on the basis of the hydrogeomorphic classification of rivers. We suggest this link can be useful in fair asset trading (mitigation and offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of rivers.
ABSTRACT The interplay of hydrology, geomorphology, and ecology within an aquatic-terrestrial lan... more ABSTRACT The interplay of hydrology, geomorphology, and ecology within an aquatic-terrestrial landscape makes floodplain rivers among the world's most complex ecosystems. Their spatial and temporal variability create diverse communities with complex trophic interactions. Floodplain-rivers are, unfortunately, also among those environments most heavily impacted by human activities. Analysis of the extent of ecological change in these rivers as a direct result of altered hydrological and geomorphological conditions is typically limited to short-term, post-impact studies or comparisons between "similar" disturbed and undisturbed rivers. We used museum specimens of fish to develop a +70-yr timeline of carbon and nitrogen stable isotope ratios to quantify the response of the trophic organization of fish communities to changes in hydrological character below the last of the dams impounding the Missouri River, USA. Isotopic ratios of fish representative of four feeding guilds were used to calculate community measures of trophic structure. A series of hydrological indices, calculated from historical discharge data, were used to determine if alteration of hydrological conditions have influenced the trophic structure within the fish community. Data were examined using 5-yr intervals over the period for which museum specimens were available (1930-1989), with dam operation beginning 1950-1954. Hydrological indices for seasonal amplitude and seasonal periodicity exhibited the greatest change from the pre-dam to post-dam periods. This resulted from reduced peak flows and higher seasonal low flows, coupled with reversal of the annual high- and low-flow periods. Total community niche space and distance between niches occupied by individual species within the community niche space declined following commencement of dam operations, indicating a decrease in the range of basal resources driving the food web and shortening of the food chain. Species packing, however, did not change, suggesting that competition for resources did not increase. We propose that changes in the hydrological pattern resulting from dam operation reduced connectivity between hydrogeomorphic patches within the riverine landscape, thereby limiting access to potentially higher quality resource patches. Additionally, the shift in time of year of annual peak flow potentially altered availability and quality of autochthonous and allochthonous resources during a time when biological productivity should be greatest.
ABSTRACT We are proposing an integrated, heuristic model of lotic biocomplexity that encompasses ... more ABSTRACT We are proposing an integrated, heuristic model of lotic biocomplexity that encompasses spatiotemporal scales from headwaters to large rivers and from main channels to floodplains. Our hope is that this model will provide a foundation for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. The model represents a conceptual marriage of eco-geomorphology with a terrestrial landscape model describing hierarchical patch dynamics (HPD). Contrasting with a common view of rivers as continuous, longitudinal gradients in physical conditions, our model portrays rivers as downstream arrays of large hydrogeomorphic patches formed by catchment geomorphology and climate. Unique "functional process zones" (FPZs) will be formed within individual types of hydrogeomorphic patches because of physiochemical habitat differences affecting ecosystem structure and function. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004. In Part I of our oral presentation, we will give an overview of this biocomplexity model and discuss how it varies from our perspectives on the ecology of lotic ecosystems.
An agriculturally-impacted stream in northern Idaho was examined over a two-year period to determ... more An agriculturally-impacted stream in northern Idaho was examined over a two-year period to determine seasonal and longitudinal patterns of the storage and decomposition of particulate organic matter. Biomass of benthic organic matter (BOM) was considerably less than values reported in the literature for comparable, undisturbed streams. Coarse, fine, and total benthic particulate organic matter were not correlated with parameters pertaining
Lapwai Creek, an agriculturally impacted stream in northern Idaho, was examined to determine long... more Lapwai Creek, an agriculturally impacted stream in northern Idaho, was examined to determine longitudinal patterns of particulate allochthonous input from different riparian vegetation types. The stream, characterized by extensive removal of mature vegetation, was classified as having four riparian vegetation types: herbaceous, herbaceous-shrub mix, shrubs, and deciduous trees. Litterfall from each vegetation type was measured monthly for two years at
The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual pre... more The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25232 m31s on the upper Mississippi and 21240 m3 Is on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river-floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately for each river, indicated there were few interannual differences in 1513C and 1515N of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between-year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years, with fine and ultra-fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in 15 13C and 1515N between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright
The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual pre... more The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25232 m31s on the upper Mississippi and 21240 m3 Is on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river-floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately for each river, indicated there were few interannual differences in 1513C and 1515N of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between-year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years, with fine and ultra-fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in 15 13C and 1515N between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright
We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales fro... more We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales from headwaters to large rivers. This riverine ecosystem synthesis (RES) provides a framework for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. Rather than posing a completely new model, we arrange a conceptual marriage of eco-geomorphology (ecological aspects of fluvial geomorphology) with a terrestrial landscape model describing hierarchical patch dynamics. We modify five components of this terrestrial model for lotic ecosystems: (1) nested, discontinuous hierarchies of patch mosaics; (2) ecosystem dynamics as a composite of intra-and inter-patch dynamics; (3) linked patterns and processes; (4) dominance of non-equilibrial and stochastic processes; and (5) formation of a quasi-equilibrial, metastable state. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004.
Analyses of stable isotope (delta(13)C and delta(15)N) and C:N ratios of food webs within a flood... more Analyses of stable isotope (delta(13)C and delta(15)N) and C:N ratios of food webs within a floodplain and a constricted-channel region of the Ohio River during October 1993 and July 1994 indicate that the increasingly influential flood pulse concept (FPC) does not, for either location, adequately address food web structure for this very large river. Furthermore, results of this study suggest that the riverine productivity model (RPM) is more appropriate than the widely known river continuum concept (RCC) for the constricted region of this river. These conclusions are based on stable isotope analyses of potential sources of organic matter (riparian C-3 trees, riparian C-4 grasses and agricultural crops, submerged macrophytes, benthic filamentous algae, benthic particulate organic matter, and transported organic matter containing detritus and phytoplankton) and various functional feeding groups of invertebrate and fish consumers. The FPC, which stresses the key contribution of organic matter, particularly terrestrial organic matter, originating from the floodplain to riverine food webs, was judged inappropriate for the floodplain region of the Ohio River for hydrodynamic and biotic reasons. The rising limb and peak period of discharge typically occur in November through March when temperatures are low (generally much less than 10 degrees C) and greater than bank-full conditions are relatively unpredictable and short-lived. The major food potentially available to riverine organisms migrating into the floodplain would be decaying vegetation because autotrophic production is temperature and light limited and terrestrial insect production is minimal at that time. It is clear from our data that terrestrial C-4 plants contribute little, if anything, to the consumer food web (based on delta(13)C values), and delta(15)N values for C-3 plants, coarse benthic organic matter, and fine benthic organic matter were too depleted (similar to 7-12 parts per thousand, lower than most invertebrate consumer values) for this organic matter to be supporting the food web. The RPM, which emphasizes the primary role of autotrophic production in large rivers, is the most viable of the remaining two ecosystem models for the constricted-channel region of the Ohio based on stable isotope linkage between sources and consumers of organic matter in the food web. The most important form of food web organic matter is apparently transported (suspended) fine (FTOM) and ultra-fine particulate organic matter. We propose that phytoplankton and detritus of an autochthonous origin in the seston would rep resent a more usable energy source for benthic (bivalve molluscs, hydropsychid caddisflies) and planktonic (microcrustaceans) suspension feeders than the more refractory allochthonous materials derived from upstream processing of terrestrial organic matter. Benthic grazers depend heavily on nonfilamentous benthic algae (based on gut analysis from a separate study), but filamentous benthic algae have no apparent connection to invertebrate consumers (based on delta(13)C values). Amphipod and crayfish show a strong relationship to aquatic macrophytes (possibly through detrital organic matter rather than living plant tissue). These observations contrast with the prediction of the RCC that food webs in large rivers are based principally on refractory FTOM and dissolved organic matter from upstream inefficiencies in organic-matter processing and the bacteria growing upon these suspended or dissolved detrital compounds.
The conclusions drawn here for the Ohio River cannot yet be extended to other floodplain and constricted-channel rivers in temperate and tropical latitudes until more comparable data are available on relatively pristine and moderately regulated rivers.
Trophic dynamics of large river-floodplain ecosystems are still not well understood despite devel... more Trophic dynamics of large river-floodplain ecosystems are still not well understood despite development of several conceptual models over the last 25 years. To help resolve questions about the relative contribution of algal and detrital organic matter to food webs in the Upper Mississippi River, we (1) separated living and detrital components of ultrafine and fine transported organic matter (UTOM and FTOM, respectively) by colloidal silica centrifugation; (2) identified stable isotope signatures (d 13 C and d 15 N) for these two portions of transported organic matter and other potential organic matter sources; and (3) employed a multiple source, dual-isotope mixing model to determine the relative contribution of major energy sources to primary consumers and the potential contribution of basal sources to the biomass of secondary consumers. The d 13 C and d 15 N of living and detrital fractions of UTOM and FTOM were distinct, indicating clear differences in isotopic composition of the algal and detrital fractions of transported organic matter. Living and detrital transported organic matter also differed from other potential organic matter sources by either d 13 C or d 15 N. A six-source mixing model using both d 13 C and d 15 N indicated that algal transported organic matter was the major resource assimilated by primary consumers. The contribution of detrital transported organic matter was small in most cases, but there were a small number of taxa for which it could potentially contribute to more than half the assimilated diet. Colloidal dissolved organic matter, which includes heterotrophic bacteria, accounted for only a small fraction of the organic matter assimilated by most primary consumers, indicating that coupling between microbial processes and metazoan production is minimal. Terrestrial C 3 litter from the floodplain forest floor and aquatic macrophytes were also relatively unimportant to the assimilated diet of primary consumers. Application of the mixing model to compare basal source isotopic ratios to secondary consumers revealed that most organic matter moving from primary to secondary consumers originated from algal TOM. Our findings indicate that autochthonous organic matter is the major energy source supporting metazoan production in the main channel of this large river, at least during the summer. This study joins a number of other investigations performed globally that indicate organic matter originating from instream production of sestonic and benthic microalgae is a major driver in the trophic dynamics of large river ecosystems.
1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hy... more 1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hydrological connectivity from maximum connection in main channel habitats to minimum connection in backwaters. Spatiotemporal differences in water currents along this gradient produce dynamic habitat conditions that influence species diversity, population densities and trophic interactions of fishes. 2. We examined the importance of lateral connectivity gradients for food web dynamics in the Upper Mississippi River during spring (high flow, moderately low temperatures) and summer (low flow, higher temperatures). We used literature information and gut contents analyses to determine feeding guilds and stable isotope analysis to estimate mean trophic position of local fish assemblages. During June and August 2006, we collected over 1000 tissue samples from four habitats (main channel, secondary channels, tertiary channels and backwaters) distributed within four hydrologic connectivity gradients. 3. Mean trophic position differed among feeding guilds and seasons, with highest values in spring. Mean trophic position of fish assemblages, variability in trophic position and food chain length (maximum trophic position) of the two dominant piscivore species (Micropterus salmoides and M. dolomieu) in both seasons were significantly associated with habitat along the lateral connectivity gradient. Food chain length peaked in tertiary channels in both seasons, probably due to higher species diversity of prey at these habitats. We infer that food chain length and trophic position of fish assemblages were lower in backwater habitats in the summer mainly because of the use of alternative food sources in these habitats. 4. A greater number of conspecifics exhibited significant among-habitat variation in trophic position during the summer, indicating that low river stages can constrain fish movements in the Upper Mississippi River. 5. Results of this study should provide a better understanding of the fundamental structure of large river ecosystems and an improved basis for river rehabilitation and management through knowledge of the importance of lateral complexity in rivers.
Assignment of values for natural ecological benefits and anthropocentric ecosystem services in ri... more Assignment of values for natural ecological benefits and anthropocentric ecosystem services in riverine landscapes has been problematic, because a
firm scientific basis linking these to the river’s physical structure has been absent.We highlight some inherent problems in this process and suggest
possible solutions on the basis of the hydrogeomorphic classification of rivers.We suggest this link can be useful in fair asset trading (mitigation and
offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of
rivers.
Assignment of values for natural ecological benefits and anthropocentric ecosystem services in ri... more Assignment of values for natural ecological benefits and anthropocentric ecosystem services in riverine landscapes has been problematic, because a firm scientific basis linking these to the river's physical structure has been absent. We highlight some inherent problems in this process and suggest possible solutions on the basis of the hydrogeomorphic classification of rivers. We suggest this link can be useful in fair asset trading (mitigation and offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of rivers.
ABSTRACT The interplay of hydrology, geomorphology, and ecology within an aquatic-terrestrial lan... more ABSTRACT The interplay of hydrology, geomorphology, and ecology within an aquatic-terrestrial landscape makes floodplain rivers among the world's most complex ecosystems. Their spatial and temporal variability create diverse communities with complex trophic interactions. Floodplain-rivers are, unfortunately, also among those environments most heavily impacted by human activities. Analysis of the extent of ecological change in these rivers as a direct result of altered hydrological and geomorphological conditions is typically limited to short-term, post-impact studies or comparisons between "similar" disturbed and undisturbed rivers. We used museum specimens of fish to develop a +70-yr timeline of carbon and nitrogen stable isotope ratios to quantify the response of the trophic organization of fish communities to changes in hydrological character below the last of the dams impounding the Missouri River, USA. Isotopic ratios of fish representative of four feeding guilds were used to calculate community measures of trophic structure. A series of hydrological indices, calculated from historical discharge data, were used to determine if alteration of hydrological conditions have influenced the trophic structure within the fish community. Data were examined using 5-yr intervals over the period for which museum specimens were available (1930-1989), with dam operation beginning 1950-1954. Hydrological indices for seasonal amplitude and seasonal periodicity exhibited the greatest change from the pre-dam to post-dam periods. This resulted from reduced peak flows and higher seasonal low flows, coupled with reversal of the annual high- and low-flow periods. Total community niche space and distance between niches occupied by individual species within the community niche space declined following commencement of dam operations, indicating a decrease in the range of basal resources driving the food web and shortening of the food chain. Species packing, however, did not change, suggesting that competition for resources did not increase. We propose that changes in the hydrological pattern resulting from dam operation reduced connectivity between hydrogeomorphic patches within the riverine landscape, thereby limiting access to potentially higher quality resource patches. Additionally, the shift in time of year of annual peak flow potentially altered availability and quality of autochthonous and allochthonous resources during a time when biological productivity should be greatest.
ABSTRACT We are proposing an integrated, heuristic model of lotic biocomplexity that encompasses ... more ABSTRACT We are proposing an integrated, heuristic model of lotic biocomplexity that encompasses spatiotemporal scales from headwaters to large rivers and from main channels to floodplains. Our hope is that this model will provide a foundation for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. The model represents a conceptual marriage of eco-geomorphology with a terrestrial landscape model describing hierarchical patch dynamics (HPD). Contrasting with a common view of rivers as continuous, longitudinal gradients in physical conditions, our model portrays rivers as downstream arrays of large hydrogeomorphic patches formed by catchment geomorphology and climate. Unique "functional process zones" (FPZs) will be formed within individual types of hydrogeomorphic patches because of physiochemical habitat differences affecting ecosystem structure and function. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004. In Part I of our oral presentation, we will give an overview of this biocomplexity model and discuss how it varies from our perspectives on the ecology of lotic ecosystems.
An agriculturally-impacted stream in northern Idaho was examined over a two-year period to determ... more An agriculturally-impacted stream in northern Idaho was examined over a two-year period to determine seasonal and longitudinal patterns of the storage and decomposition of particulate organic matter. Biomass of benthic organic matter (BOM) was considerably less than values reported in the literature for comparable, undisturbed streams. Coarse, fine, and total benthic particulate organic matter were not correlated with parameters pertaining
Lapwai Creek, an agriculturally impacted stream in northern Idaho, was examined to determine long... more Lapwai Creek, an agriculturally impacted stream in northern Idaho, was examined to determine longitudinal patterns of particulate allochthonous input from different riparian vegetation types. The stream, characterized by extensive removal of mature vegetation, was classified as having four riparian vegetation types: herbaceous, herbaceous-shrub mix, shrubs, and deciduous trees. Litterfall from each vegetation type was measured monthly for two years at
The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual pre... more The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25232 m31s on the upper Mississippi and 21240 m3 Is on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river-floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately for each river, indicated there were few interannual differences in 1513C and 1515N of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between-year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years, with fine and ultra-fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in 15 13C and 1515N between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright
The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual pre... more The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25232 m31s on the upper Mississippi and 21240 m3 Is on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river-floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately for each river, indicated there were few interannual differences in 1513C and 1515N of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between-year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years, with fine and ultra-fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in 15 13C and 1515N between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright
We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales fro... more We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales from headwaters to large rivers. This riverine ecosystem synthesis (RES) provides a framework for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. Rather than posing a completely new model, we arrange a conceptual marriage of eco-geomorphology (ecological aspects of fluvial geomorphology) with a terrestrial landscape model describing hierarchical patch dynamics. We modify five components of this terrestrial model for lotic ecosystems: (1) nested, discontinuous hierarchies of patch mosaics; (2) ecosystem dynamics as a composite of intra-and inter-patch dynamics; (3) linked patterns and processes; (4) dominance of non-equilibrial and stochastic processes; and (5) formation of a quasi-equilibrial, metastable state. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004.
Analyses of stable isotope (delta(13)C and delta(15)N) and C:N ratios of food webs within a flood... more Analyses of stable isotope (delta(13)C and delta(15)N) and C:N ratios of food webs within a floodplain and a constricted-channel region of the Ohio River during October 1993 and July 1994 indicate that the increasingly influential flood pulse concept (FPC) does not, for either location, adequately address food web structure for this very large river. Furthermore, results of this study suggest that the riverine productivity model (RPM) is more appropriate than the widely known river continuum concept (RCC) for the constricted region of this river. These conclusions are based on stable isotope analyses of potential sources of organic matter (riparian C-3 trees, riparian C-4 grasses and agricultural crops, submerged macrophytes, benthic filamentous algae, benthic particulate organic matter, and transported organic matter containing detritus and phytoplankton) and various functional feeding groups of invertebrate and fish consumers. The FPC, which stresses the key contribution of organic matter, particularly terrestrial organic matter, originating from the floodplain to riverine food webs, was judged inappropriate for the floodplain region of the Ohio River for hydrodynamic and biotic reasons. The rising limb and peak period of discharge typically occur in November through March when temperatures are low (generally much less than 10 degrees C) and greater than bank-full conditions are relatively unpredictable and short-lived. The major food potentially available to riverine organisms migrating into the floodplain would be decaying vegetation because autotrophic production is temperature and light limited and terrestrial insect production is minimal at that time. It is clear from our data that terrestrial C-4 plants contribute little, if anything, to the consumer food web (based on delta(13)C values), and delta(15)N values for C-3 plants, coarse benthic organic matter, and fine benthic organic matter were too depleted (similar to 7-12 parts per thousand, lower than most invertebrate consumer values) for this organic matter to be supporting the food web. The RPM, which emphasizes the primary role of autotrophic production in large rivers, is the most viable of the remaining two ecosystem models for the constricted-channel region of the Ohio based on stable isotope linkage between sources and consumers of organic matter in the food web. The most important form of food web organic matter is apparently transported (suspended) fine (FTOM) and ultra-fine particulate organic matter. We propose that phytoplankton and detritus of an autochthonous origin in the seston would rep resent a more usable energy source for benthic (bivalve molluscs, hydropsychid caddisflies) and planktonic (microcrustaceans) suspension feeders than the more refractory allochthonous materials derived from upstream processing of terrestrial organic matter. Benthic grazers depend heavily on nonfilamentous benthic algae (based on gut analysis from a separate study), but filamentous benthic algae have no apparent connection to invertebrate consumers (based on delta(13)C values). Amphipod and crayfish show a strong relationship to aquatic macrophytes (possibly through detrital organic matter rather than living plant tissue). These observations contrast with the prediction of the RCC that food webs in large rivers are based principally on refractory FTOM and dissolved organic matter from upstream inefficiencies in organic-matter processing and the bacteria growing upon these suspended or dissolved detrital compounds.
The conclusions drawn here for the Ohio River cannot yet be extended to other floodplain and constricted-channel rivers in temperate and tropical latitudes until more comparable data are available on relatively pristine and moderately regulated rivers.
Trophic dynamics of large river-floodplain ecosystems are still not well understood despite devel... more Trophic dynamics of large river-floodplain ecosystems are still not well understood despite development of several conceptual models over the last 25 years. To help resolve questions about the relative contribution of algal and detrital organic matter to food webs in the Upper Mississippi River, we (1) separated living and detrital components of ultrafine and fine transported organic matter (UTOM and FTOM, respectively) by colloidal silica centrifugation; (2) identified stable isotope signatures (d 13 C and d 15 N) for these two portions of transported organic matter and other potential organic matter sources; and (3) employed a multiple source, dual-isotope mixing model to determine the relative contribution of major energy sources to primary consumers and the potential contribution of basal sources to the biomass of secondary consumers. The d 13 C and d 15 N of living and detrital fractions of UTOM and FTOM were distinct, indicating clear differences in isotopic composition of the algal and detrital fractions of transported organic matter. Living and detrital transported organic matter also differed from other potential organic matter sources by either d 13 C or d 15 N. A six-source mixing model using both d 13 C and d 15 N indicated that algal transported organic matter was the major resource assimilated by primary consumers. The contribution of detrital transported organic matter was small in most cases, but there were a small number of taxa for which it could potentially contribute to more than half the assimilated diet. Colloidal dissolved organic matter, which includes heterotrophic bacteria, accounted for only a small fraction of the organic matter assimilated by most primary consumers, indicating that coupling between microbial processes and metazoan production is minimal. Terrestrial C 3 litter from the floodplain forest floor and aquatic macrophytes were also relatively unimportant to the assimilated diet of primary consumers. Application of the mixing model to compare basal source isotopic ratios to secondary consumers revealed that most organic matter moving from primary to secondary consumers originated from algal TOM. Our findings indicate that autochthonous organic matter is the major energy source supporting metazoan production in the main channel of this large river, at least during the summer. This study joins a number of other investigations performed globally that indicate organic matter originating from instream production of sestonic and benthic microalgae is a major driver in the trophic dynamics of large river ecosystems.
1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hy... more 1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hydrological connectivity from maximum connection in main channel habitats to minimum connection in backwaters. Spatiotemporal differences in water currents along this gradient produce dynamic habitat conditions that influence species diversity, population densities and trophic interactions of fishes. 2. We examined the importance of lateral connectivity gradients for food web dynamics in the Upper Mississippi River during spring (high flow, moderately low temperatures) and summer (low flow, higher temperatures). We used literature information and gut contents analyses to determine feeding guilds and stable isotope analysis to estimate mean trophic position of local fish assemblages. During June and August 2006, we collected over 1000 tissue samples from four habitats (main channel, secondary channels, tertiary channels and backwaters) distributed within four hydrologic connectivity gradients. 3. Mean trophic position differed among feeding guilds and seasons, with highest values in spring. Mean trophic position of fish assemblages, variability in trophic position and food chain length (maximum trophic position) of the two dominant piscivore species (Micropterus salmoides and M. dolomieu) in both seasons were significantly associated with habitat along the lateral connectivity gradient. Food chain length peaked in tertiary channels in both seasons, probably due to higher species diversity of prey at these habitats. We infer that food chain length and trophic position of fish assemblages were lower in backwater habitats in the summer mainly because of the use of alternative food sources in these habitats. 4. A greater number of conspecifics exhibited significant among-habitat variation in trophic position during the summer, indicating that low river stages can constrain fish movements in the Upper Mississippi River. 5. Results of this study should provide a better understanding of the fundamental structure of large river ecosystems and an improved basis for river rehabilitation and management through knowledge of the importance of lateral complexity in rivers.
Assignment of values for natural ecological benefits and anthropocentric ecosystem services in ri... more Assignment of values for natural ecological benefits and anthropocentric ecosystem services in riverine landscapes has been problematic, because a
firm scientific basis linking these to the river’s physical structure has been absent.We highlight some inherent problems in this process and suggest
possible solutions on the basis of the hydrogeomorphic classification of rivers.We suggest this link can be useful in fair asset trading (mitigation and
offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of
rivers.
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Papers by Michael Delong
The conclusions drawn here for the Ohio River cannot yet be extended to other floodplain and constricted-channel rivers in temperate and tropical latitudes until more comparable data are available on relatively pristine and moderately regulated rivers.
firm scientific basis linking these to the river’s physical structure has been absent.We highlight some inherent problems in this process and suggest
possible solutions on the basis of the hydrogeomorphic classification of rivers.We suggest this link can be useful in fair asset trading (mitigation and
offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of
rivers.
The conclusions drawn here for the Ohio River cannot yet be extended to other floodplain and constricted-channel rivers in temperate and tropical latitudes until more comparable data are available on relatively pristine and moderately regulated rivers.
firm scientific basis linking these to the river’s physical structure has been absent.We highlight some inherent problems in this process and suggest
possible solutions on the basis of the hydrogeomorphic classification of rivers.We suggest this link can be useful in fair asset trading (mitigation and
offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of
rivers.